Laser-induced damage thresholds of optical coatings at different temperature

Laser-induced damage thresholds for dielectric and metal single-layer coatings at different temperature conditions (123-473 K) were measured by 1064-nm wavelength and 4-ns pulses to elucidate the effects of initial temperature to laser damage mechanisms. SiO2, MgF2, gold, silver and copper single-layer coatings were prepared as experimental samples. In the experimental results, temperature dependence of LIDTs for optical substrates and all dielectric single-layer coatings indicated same trend as that for bulk silica glasses, which increased linearly with decreasing the temperature. However, all metallic coatings had the inverse trend of the dependence for dielectric coatings. The effects of initial temperature to laser damage mechanisms were considered with separated processes from the experimental results. In the conclusions, free-electron generation and electron multiple caused difficultly at low temperature and the laser-induced damage thresholds increased. On the other hand, plasma heating caused easily at low temperature and the laser-damage thresholds decreased.